1. Field of the Invention
The present invention relates to a vertebra segmentation apparatus, a vertebra segmentation method, and a recording medium storing a program for partitioning and recognizing a plurality of vertebrae from a three-dimensional medical image that includes such vertebrae.
2. Description of the Related Art
Heretofore, there have been proposed in the medical field a variety of image processing algorithms for partitioning and recognizing a plurality of vertebrae based on tomographic images generated by scanning a subject from a chest region to the legs at a plurality of sectional positions. Such an image processing sequence is referred to as “vertebra segmentation”.
“Quantitative Evaluation of Osteoporosis Likelihood using Multi-slice CT Images,” the Institute of Electronics, Information and Communication Engineers Technical Report MI2005-90, pp. 97-100, January 2006, discloses a method of partitioning and recognizing vertebrae by estimating reference positions of respective intervertebral disc regions based on an average density profile along a spinal central line, and thereafter extracting vertebral body endplates and intervertebral discs according to an appropriate morphological process performed on tomographic images near such reference positions.
“Automated Spine Column Extraction and Partition,” In 3rd IEEE International Symposium on Biomedical Imaging, pp. 390-393 (2006) discloses a method of partitioning and recognizing vertebrae by generating sagittal and coronal CRP (Curved Planar Reformation) images along a spinal central line, and extracting intervertebral discs based on a density value integral profile of tomographic images to which the spinal central line is normal.
It is generally known that if slices are thick in the scanning direction, i.e., the direction of the body axis, then the spatial resolution along the direction of the body axis becomes insufficient due to a partial volume effect, resulting in a reduction in the image rendering capability. It is particularly difficult to render intervertebral discs and vertebral body endplates separately on tomographic images within a range from the cervical vertebrae to the upper thoracic vertebrae, where each of the vertebrae is relatively short. As a result, the ability to detect intervertebral discs (i.e., the positional accuracy at which each vertebra is partition and recognized) is lowered.
As disclosed in Japanese Laid-Open Patent Publication No. 2009-207727, the inventor of the present invention has invented a method of estimating the position of a vertebral body by detecting a central line of a vertebra, then calculating a feature quantity representative of a density gradient in the direction of the body axis near the central line, specifying the central position of a vertebral body based on the feature quantity, and thereafter estimating the position of an intervertebral disc. According to this method, since the position of the intervertebral disc is estimated based on a vertebral cavernous region (hollow vertebral region), which is more detectable than the intervertebral disc, the positional accuracy at which each vertebra is partition and recognized is increased.
As disclosed in Japanese Laid-Open Patent Publication No. 2008-093254, the inventor of the present invention also has invented a display method of adding given mark images to corresponding locations on a plurality of different types of tomographic images, e.g., a combination of sagittal and coronal images, when the tomographic images are displayed adjacent to each other. Such a display method allows the user to accurately spot the position of a focus, for example.